Question Answering Request Handler example for blob store ref guide

gistfile1.java

package org.apache.solr.core;

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
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 *     http://www.apache.org/licenses/LICENSE-2.0
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 * distributed under the License is distributed on an "AS IS" BASIS,
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 * See the License for the specific language governing permissions and
 * limitations under the License.
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import java.util.ArrayList;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import org.apache.solr.common.params.ModifiableSolrParams;
import org.apache.solr.common.params.SolrParams;
import org.apache.solr.handler.StandardRequestHandler;
import org.apache.solr.request.SolrQueryRequest;
import org.apache.solr.response.SolrQueryResponse;

public class QuestionAnswerRequestHandler extends StandardRequestHandler {
  
  List<QAPattern> patterns = new ArrayList<QuestionAnswerRequestHandler.QAPattern>();
  
  public QuestionAnswerRequestHandler() {
    // Date of birth patterns
    patterns.add(new QAPattern("(when was )(.*)( born)", 2, "name_t:'ENTITY' AND type_s:person", "dob_dt"));
    patterns.add(new QAPattern("(what is the birthdate of )(.*)", 2, "name_t:'ENTITY' AND type_s:person", "dob_dt"));
    patterns.add(new QAPattern("(birthday of )(.*)", 2, "name_t:'ENTITY' AND type_s:person", "dob_dt"));
    patterns.add(new QAPattern("(how old is )(.*)", 2, "name_t:'ENTITY' AND type_s:person", "dob_dt"));
    patterns.add(new QAPattern("(what is the age of )(.*)", 2, "name_t:'ENTITY' AND type_s:person", "dob_dt"));

    // Location/hometown patterns
    patterns.add(new QAPattern("(where does )(.*)(live)", 2, "name_t:'ENTITY' AND type_s:person", "hometown_s"));
    patterns.add(new QAPattern("(hometown of )(.*)", 2, "name_t:'ENTITY' AND type_s:person", "hometown_s"));
    
    // Capital of a country
    patterns.add(new QAPattern("(capital of )(.*)", 2, "name_t:'ENTITY' AND type_s:country", "capital_s"));
    patterns.add(new QAPattern("(what is capital of )(.*)", 2, "name_t:'ENTITY' AND type_s:country", "capital_s"));
    patterns.add(new QAPattern("(what is the capital of )(.*)", 2, "name_t:'ENTITY' AND type_s:country", "capital_s"));
  }
  
  @Override
  public void handleRequestBody(SolrQueryRequest req, SolrQueryResponse rsp) throws Exception {
    SolrParams params = req.getOriginalParams();
    ModifiableSolrParams mparams = new ModifiableSolrParams(params);

    String question = params.get("q");
    if(question==null)
      return;

    for(QAPattern pat: patterns) {
      if(pat.doesMatch(question)) {
        String q = pat.getQuery(question);
        String fl = "id,name_t,"+pat.returnField;

        mparams.set("q", q, "fl", fl);
        req.forward("standard", mparams, rsp);
        return;
      }
    }
    
    // if nothing works, fall back to textual search
    mparams.set("q", "description_t:'question'", "fl", "*");
    req.forward("standard", mparams, rsp);
  }

  @Override
  public String getDescription() {
    return "Question answering query parser, accepts the question with 'q' parameter";
  }
  

  class QAPattern {
    Pattern pattern;
    int entityGroup; 
    String query; 
    String returnField;
    
    public QAPattern(String regex, int entityGroup, String queryPattern, String returnField) {
      this.entityGroup = entityGroup;
      this.query = queryPattern;
      this.returnField = returnField;
      this.pattern = Pattern.compile(regex);
    }
    
    String getQuery(String input) {
      String entity = extractEntity(input);
      if(entity==null)
        return null;
      return query.replaceAll("ENTITY", entity);
    }

    String extractEntity(String input) {
      Matcher mat = pattern.matcher(input);
      if(mat.find())
        return mat.group(entityGroup);
      return null;
    }

    boolean doesMatch(String input) {
      Matcher mat = pattern.matcher(input);
      return mat.matches();
    }
  }
  
}